Corrugated fiberboard

ABSTRACT

Corrugated fiberboard which resists deterioration in strength when in the presence of moisture or water, and intermediate resin treated medium and liner sheet members useful in the manufacture thereof. Such board is made by treating medium and, optionally, liner members with a modified phenol aldehyde resole resin composition and thereafter bonding corrugated medium to liner members with a thermosetting urea-starch-formaldehyde adhesive system.

Uited States Patent [72] Inventor Abraham J. Reisman Springfield, Mass.[21] App]. No. 843,130 [22] Filed July 18, 1969 [45] Patented Oct. 26,1971 [73] Assignee Atton Box Board Company Alton, Ill.

[54] CORRUGATED FIBERBOARD 4 Claims, 2 Drawing Figs.

[52] 11.8. Cl 161/133, 117/155 L, 161/264, 260/293, 260/515, 260/840[51] Int. Cl B321) 3/28, 1332b 27/42,C08g 37/16 [50] Field ofSearch117/155 L; 161/133, 269; 260/293, 515, 840

[56] References Cited UNITED STATES PATENTS 1,944,143 1/1934 Bender161/264X 2,334,904 1 1/1943 Cheetham 260/840 2,463,148 3/1949 Caesar etal. 260/l7.3 2,886,540 5/1959 McNaughton et al. 260/172 (S) 3,006,87910/1961 Ryan et a1 ,4 260/293 3,223,668 12/1965 Stalego 260/840 X3,380,877 4/1968 Smucker et al. 260/515 X 3,431,162 3/1969 Morris161/133 3,444,119 5/1969 LeBlanc 260/293 2,886,541 5/1959 Langlois eta]260/172 (S) Primary ExaminerRobert F. Burnett Assistant Examiner-StephenM. Hoffman Attorneys-John W. Klooster, Arthur E. Hoffman and Russell H.Schlattman PAIENTEIIIIBI 2 s ISTI 3, 6 1. 6 l 6 3 TREAT LINER WITH TREATMEDIUM TREAT LINER WITH RESIN (OPTIONAL) WITH RESIN RESIN (OPTIONAL) I II DRY TO PRESET DRY TO PRESET DRY TO PRESET VOLATILES CONTENT VOLATILESCONTENT VOLATILES CONTENT CORRUGATE MEDIUM AND APPLY ADHESIVE TO FLUTESTHEREOF I MAKE CARTON BLANKS (FOLD, SCORE, CUT, ETC.)

HEAT TREAT BLANKS TO CURE RESIN (OPTIONAL) HUMIDIFY BLANKS F|G 2(OPTIONAL) ASSEMBL E BLANKS INVENTOR INTO CARTONS ABRAHAM J. REISMANJOHN w. KLOOSTER, BY ARTHUR E. HOFFMAN,

RUSSELL H. SCHLATTMAN ATTORNEYS BACKGROUND Corrugated fiberboard hasbeen used for many years and for various purposes, but is well known tohave poor wet strength properties. However, for some time, manufacturersof corrugated fiberboard have tried to remedy such inherent deficienciesin wet strength (as determined, for example, using postmoisture exposurecrush resistance comparative measure ments) by impregnating the papersheeting used in making such board with various polymeric substancesincluding phenolic resins. So far as is known, however, such effortshave not been successful in producing corrugated fiberboard ofcommercially useful quality; see, for example, Koning, Jr. and Fahey ofthe US. Forest Products Laboratory reported in Package Engineering,"Vol. 10, Oct. 1965, at pages 130 through 139.

Such previous efforts to improve wet strength using phenolaldehyderesins have generally not been successful because of a variety ofproblems, such as:

A. the prolonged and excessively high temperatures required forphenol-aldehyde resin curing (preventing the use in effect of phenolicresins on the high speed machinery conventionally commercially used tomake corrugated fiberboard);

B. the inability of conventional aqueous phenol-aldehyde resin systemsto uniformly penetrate base paper stock during high-speed treating;

C. the embrittlement and even partial decomposition commonly associatedwith paper stock following phenol-aldehyde resin treatment andincorporation into corrugated fiberboard;

D. the lack of compatibility and good bonding between phenol-aldehydethermoset resin treated base stock and adhesive systems used to bondsuch resin treated medium and liner sheets together into corrugatedfiberboard; and the like.

It has surprisingly and unexpectedly how been discovered that each ofsuch prior art problems can be overcome when a particular modifiedphenol-aldehyde resin system and a particular adhesive system are usedin conventional high-speed manufacturing equipment to make corrugatedfiberboard having among other desirable properties generally superiorpostmoisture exposure crush resistance.

A significant advantage associated with the present invention is thatthe resin system used for impregnation of the base prior stock used insuch fiberboard manufacture thermosets at significantly highertemperatures using shorter times than those needed to thermoset theadhesive system employed, thereby making it possible if desired tomaximize wet strength in a product carton blank to first cure theadhesive used to make the board, then form the blank from the board, andfinally cure the resin in the paper used to make the board rather thancuring adhesive and resin in board manufacture. Consequently, one can,if desired, first manufacture corrugated fiberboard having good drystrength and flexibility characteristics, such as are desirable infurther machine processing of corrugated fiberboard into manufacturedarti cles like box blanks, etc., and then process such fiberboard intosuch manufactured articles. Thereafter, the impregnated resin can bethermoset, and the resulting corrugated fiberboard accordingly stiffenedand rigidified by raising the so-manufactured articles to temperatureshigh enough to thermoset such impregnated resin.

it is during this last heating (thermosetting) step that anothersignificant advantage of our invention is appreciated: The particularresin employed in our invention thermosets so rapidly that the desired,normal, inherent moisture content of corrugated fiberboard is notdepleted or reduced to the point where the product board is excessivelyand even permanently embrittled, which was a common fault with prior arttreating resins.

Another advantage is that during thermosetting of impregnated resin andof adhesive, there is a low evolution of free formaldehyde intoadjoining environment, with consequent unpleasant and even toxic fumesbeing foisted upon personnel.

Other and further advantages will be apparent to those skilled in theart from the present teachings.

SUMMARY The present invention relates to a novel corrugated fiberboardconstruction adapted to have good wet strength, and to certain novelresin treated medium and liner sheet members useful as intermediates forthe manufacture of such fiberboard. For purposes of the presentinvention, wet strength of corrugated fiberboard is convenientlymeasured comparatively using flat crush resistance data before and aftermoisture exposure by means of ASTM Test Procedure No. D-l225-D) Anintermediate sheet member of this invention which is adapted for use asa medium in the manufacture of corrugated fiberboard utilizes apaperboard ranging in thickness from about 7 to 15 thousandths of aninch and having a grade weight of from about 25 to 36 pounds per 1,000sq. ft.

Such a paper has been treated with from about 5 to 15 weight percenttotal (dry weight basis) of a modified phenolaldehyde resin system andsaid paper afier such treatment has a total volatiles content of fromabout 5 to 10 weight percent.

The terms treated, treating," or "treatment" as used herein is genericto both impregnation and coating of the substrate paper itself; such canbe accomplished in any convenient, conventional manner, as hereinafterfurther detailed and illustrated.

An intermediate sheet member of this invention which is adapted for useas a liner in the manufacture of corrugated fiberboard utilizes a paperboard ranging in thickness from about 5-20 thousandths of an inch andhaving a grade weight offrom about 33 to 120 pounds per 1,000 sq. ft.

Such a paper has been treated with from about 2 to 10 weight percent(total dry weight basis) of such a modified phenol-aldehyde resin systemand said paper after such treatment has a total volatiles content offrom about 5 to 10 weight percent.

Liner sheet members used in the novel corrugated fiberboardconstructions of this invention need not be, but preferably are, treatedwith such a modified phenolaldehyde resin system.

A corrugated fiberboard construction of this invention employs a treatedmedium, as above described, and a liner (preferably, though notnecessarily, a treated one, as above described). Each such medium iscorrugated and positioned adjacent to a liner member on one side thereof(preferably there is a liner in each side of a corrugated medium). Eachliner is bonded to its adjoining medium at positions of mutual contacttherebetween with an adhesive which is interposed between such a linersheet member and such a medium sheet member at such positions of mutualcontact (typically the tips ofthe corrugated medium flutes).

The modified phenol-aldehyde resin system used comprises:

A. from about 80 to 94 weight percent (based on total modifiedphenol-aldehyde resin system dry weight basis) of a phenol-formaldehyderesole resin,

B. from about 1 to 5 weight percent (same basis) of at least oneinorganic ammonium salt having a pH of from about 0.8

to 6.5 when in a 5 weight percent aqueous solution, such as, forexample, ammonium chloride (preferred), and other ammonium halides,ammonium sulfate, ammonium phosphate (including acid salts thereof),ammonium nitrate, and the like,

C. the remainder up to weight percent (same basis) of any given suchsystem of urea. This resin system has a pH in the range of from about0.8 to six (preferably about 1 to 4) when the form of an aqueoussolution of about 35 weight percent total resin system solids.

The phenol-formaldehyde resole resin used in this resin system is itselfcharacterized by having:

A. a water solubility such that about a 55 weight percent aqueoussolution of resole resin solids can be prepared,

B. a combined average number of mols of formaldehyde per phenol ring offrom about 0.9 to 3.0,

C. a pH of from about 7 to 9.2 when in the form of an aqueous solutionof about 35 weight percent total resin solids, and

D. an ash content of less than about 2.5 weight percent (based on abouta 35 weight percent solution of total resin solids).

The adhesive used comprises a urea-starch-formaldehyde adhesive systemcharacterized by:

' A. having a total urea to total starch weight ratio (based on totaladhesive system solids) of about i to 7,

B. containing at least about 1 weight percent (based on total adhesivesystem solids) of combined formaldehyde, and

C. containing at least about 70 weight percent of starch (based on totaladhesive systems solids).

Such adhesive system is, at the time of use to make corrugatedfiberboard of this invention, in the form of an aqueous dispersionhaving a total solids content of from about to 30 weight percent, aviscosity of from about 200 to 8000 centipoises. Starting Materials Asthose skilled in the art will appreciate, in the art of corrugatedfiberboard, it has been conventional to employ as the medium sheetmember either Kraft paper ofjute paper. A corrugated medium member isformed by running a continuous sheet of medium through corrugatingrolls. The medium, or 9 point as it is sometimes called, takes on awavelike shape as it passes between the corrugating rolls which meshsimilar to gear teeth except that they are especially shaped to providecontours deemed best by a particular manufacturer for corruga'tions.

While the corrugating medium may be any of the cellulosic fibrous sheetmaterials conventionally used in the art, it is usually a sheet of about26 pounds per 1,000 sq. ft. having a thickness of about 0.009 inch forall grades of combined board, but for purposes of the present invention,may be heavier or lighter for special requirements. Corrugating medium,for example, is most commonly made from semi-chemical pulp but is alsomade from straw, craft, bogus, or chip (mixed, repulped fibers).

There are four conventional or standard sizes of corrugations asfollows:

TABLE I Number of Flutes Thickness of Approximate, depending onthickness oft'ucings and also the particular corruguting rolls.

As with medium sheet members, any conventional liner sheet member can beused in the manufacture of the corrugated fiberboard of the presentinvention. Generally, the liner sheet members are made from sulfateKraft, but sometimes are made from other pulps.

Kraft for liner sheet members is usually made on a Fourdrinier machinealthough some is made on a cylinder machine. Commonly, liner sheetmembers are made to standard weights which are 26, 33, 38, 42, 47, 62,69, and 90 pounds per 1,000 sq. ft. with thicknesses for liner sheetmembers ranging from 0.009 inch to 0.025 inch.

Details on the characteristics of medium sheet members and liner sheetmembers are well known to the corrugated fiberboard manufacturingindustry. See, for example, Uniform Freight Classification Rule 41. Thecorrugation flutes can be combined using adhesive with a facing or linersheet member on one side only, called a single face board; when facingsare on both sides of the corrugated medium sheet member, the product issometimes called single wallboard or double face board. if there are twosheets of flutes with a facing on each side and one in the middle, theproduct is sometimes called double wallboard. if there are three layersof flutes with two outer liner facings and two inner liner facingsbetween media layers, the product is sometimes called triple wallboard.

The modified phenol-aldehyde resin system can be made by anyconventional procedure known to the art of phenolic resins. For example,one convenient and preferred procedure involves condensing usually attemperatures ranging from about 50 to Centigrade phenol and formaldehydein the above-indicated desired mol ratio under aqueous liquid phaseconditions in the presence of a basic catalyst, such as an alkali metalhydroxide such as sodium hydroxide or an alkaline earth hydroxide suchas calcium hydroxide, a trialkyl amine such as triethylamine, and thelike until a desired end point is reached, such as, for example, a freeformaldehyde content which is less than about 3 to 10 weight percent.

The product is a phenol-formaldehyde resole resin in aqueous solutionhaving a total solids content of from about 30 to 70 weight percent.Usually and preferably, the resin solution is prepared as a concentrateof from about 40 to 55 weight percent solids (based on the totalsolution weight) which may be conveniently and preferably diluted downbefore use to a solids content of from about 5-50 weight percent.Preferably, the solids content of the concentrate ranges from about45-60 weight percent and preferably the solids content of the dilutedworking solution ranges from about 15-45 weight percent.

For use in the products of this invention, it has been found that thisresole resin should not be advanced in manufacture beyond the pointwhere it has a water solubility such that about a 55 weight percentsolids in aqueous solution thereof can be prepared (preferably about 30weight percent). Also, it has been found that this resole resin shouldhave a methylol content per aromatic ring of from about 0.5 to 3(preferably from about i to 2.5) as determined, for example, by NMRmeasurements.

if such resin is more advanced (i.e. has a high molecular weight) thansuch a solubility as above indicated, or if such resin has a differentmethylol content than that above indicated, then it appears to haveundesirable paper treating characteristics, especially at the highapplication speeds conventionally employed for paper transport in themanufacture of corrugated fiberboard, for purposes of making theimproved products of this invention.

In addition, it has been found that this resole resin should have a pHof from about 5.6 to 9.2 when in the form of an aqueous solution ofabout 35 weight percent total resin solids (preferably from about 7 to8.5). Also, it has been found that this resole resin should have an ashcontent of less than about 2.5 weight percent based on about a 35 weightpercent aqueous solution of total resin solids (preferably less thanabout 0.7).

One convenient way in which to measure the ash content for presentpurposes is to take 2 grams of such an aqueous solution (35 percentsolids) and deposit same in a crucible. The crucible is then heated toabout C. for about 2 hours to substantially completely crossiink theresin and evaporate free water and thereafter the crucible is exposed toabout l,000 F. for about 24 hours. Afterwards, the crucible is cooled toroom temperature and measured to determine an increase in weight overstarting empty weight thereby giving the ash content of the resin.

if such resin has a lower or higher pH, or a higher solids content, thanthose respectively above indicated, then it appears to have undesirableeffects upon product paper treated therewith, especially in theproperties of corrugated fiberboard made therefrom, for purposes ofmaking the improved products of this invention.

in making the modified phenol-aldehyde resin systems for use in thisinvention, it is generally convenient and preferred to add the ammoniumsalt and the urea in the respective amounts above indicated, each in theform of a finely divided power, or even (preferably) already dissolvedin water, to the diluted or partially diluted phenol-formaldehyde resoleresin (just described). Such addition causes the pH of this productsystem to fall in the range from 0.8 to 6, as above described.

Sometimes in order to make the pH of the product phenolaldehyde resinsystem low, yet within the indicated range, one may, if desired, add toa given resole resin solution, preferably diluted for use and with theammonium salt and urea already dissolved therewith, amounts of a stronginorganic acid, such as hydrochloric, or the like, until the pH islowered to some desired value; however, such an acid addition isgenerally not necessary owing to the presence of the ammonium salt whichitself tends to produce a pH within the ranges indicated.

The ammonium salt and the urea are conveniently not added to the resoleresin solution until shortly before a medium or liner sheet member is tobe treated with a resin system, and they are conveniently added theretoin a previously water dissolved form.

The medium and liner can be treated with a resin system by immersion orany other convenient coating techniques. For example, in linertreatment, a preferred method involves surface coating rather thanimmersion impregnation. Suitable coating procedures involve applicationto one surface of a liner with a brush, doctor blade, or otherapplication mechanism. Such a procedure is particularly applicable whenonly one side of liner is to be treated with a resin system because acoating procedure produces a differential impregnation or coating of theliner. Thus, the resin density is then greater relative to one surfaceof the resulting liner sheet than relative to the other (opposed)surface thereof. In general, it is preferred to uniformly coat mediumsheet members with a resin system.

After treatment, a medium or liner sheet member is dried by passing suchover or through a hot zone such that the temperature of the liner and/orthe medium does not exceed about 225 F. for more than about 0.1 secondso as to avoid thermosetting the resin system. In drying, water issubstantially completely removed without appreciable advancement orcuring of the resin impregnated into the liner or medium sheet member.Thus, the percentage of volatiles in a treated liner or medium iscontrolled within the ranges above indicated. For example, if thepercentage of volatiles is reduced below such range, the resin systemtends to crosslink and subsequently during corrugated fiberboardproduction reduced adhesive bonding to such a resin crosslinked mediumor liner sheet tends to result, among other undesired results. On theother hand, for example, if the percentage of volatiles is leftappreciably above such range, reduced adhesive bonding can likewiseresult. Also, outside of these ranges, a treated medium may be difficultto corrugate. Next, if not stored interveningly, a treated medium and aliner member are combined together. Commercially, a conventionalcombining machine may be used for this operation.

The adhesive used in the combining operation is as characterized above.Such adhesives are well known to the art, but, briefly, they areprepared, for example, according to the teachings of U.S. Pat. No.2,463,148.

Typically, an adhesive used to make a corrugated fiberboard of thisinvention at the time of application to medium is in the form of anaqueous system Whose viscosity ranges from about 200 to 8,000centipoises (preferably 300 to 5,000- and which has a total solidscontent of from about to 30 weight percent. Usually, the adhesive systemis in the form ofa uniform heterogeneous aqueous dispersion in whichsome of the resin portion of the system is dissolved and some of thestarch portion is dispersed. As in the case of the resin used toimpregnate medium liner sheet members, such adhesive systems areconventional to the art and do not constitute a part of the presentinvention. In general, the adhesive used is prepared just priorto thetime of use by a fiberboard manufacturer or it is prepared by a supplierto him. Commonly, a supplier provides the adhesive as one tank or twotank formulation, which is combined in the case of two tanks, and whichis typically further diluted with water before actual application.

Although an adhesive is generally discontinuously but automaticallyapplied only to the flutes of a corrugated treated medium when usingmachinery to make corrugated fiberboard of this invention, typicalmachine adhesive application rates range from about 3 to 12 poundsadhesive solids per 1000 sq. ft. of product corrugated fiberboard butmore or less than this amount can be employed. Adhesive applicationrates are not critical and can be widely varied without departing fromthe spirit and scope of this invention.

After adhesive application, corrugated medium sheet member and linersheet member are duly combined together, as in a so-called combiningmachine, into board, the resulting fiberboard construction is subjectedto temperatures of from about 320 to 450 F. for times of from about 5seconds to 10 minutes to complete manufacture. Afterwards, the productboard can be rolled up in a storage configuration, as is commonly donein continuous corrugated fiberboard manufacture. Preferred temperaturesfor heating the combined corrugated medium sheet and liner sheet memberinvolve the use of temperatures of from about 320 to 370' IF. appliedfor times of from about 5 to 15 seconds. Such preferred heatingtemperatures and times substantially completely thermoset the adhesive,but not the resin, thus bonding together the medium and liner sheetmembers at positions of mutual contact therebetween, thereby to form adesired corrugated fiberboard. When only the adhesive is thermoset, theproduct fiberboard is generally more limber and pliable than when theresin is thermoset, which is desirable when the fiberboard product is tobe made into box blanks.

Preferably, a corrugated fiberboard construction of this invention isequipped with at least a pair of such liner sheet members so that such apreferred construction has its opposed faces composed of liner sheetmembers with a resin treated medium sheet interposed therebetween (andbonded by means of such adhesive, as indicated).

Usually, and conventionally, a corrugated fiberboard of this inventionis promptly made into box blanks following manufacture, though it ispossible and convenient to store the corrugated fiberboard before sameis used to make box blanks. Box (or carton) blank manufacture is wellknown to those of ordinary skill in the art and does not form part ofthis inven tion. When corrugated fiberboard is directly converted intobox blanks, it is conventional to place at the end of a combiningmachine knives which cut the corrugated fiberboard into the lengthsrequired by the particular box to be made. Next, the resulting piece ofboard is scored longitudinally, so as to permit folding such board tomake the top and bottom flaps of a box. In this operation, the sheet offiberboard product is also longitudinally edge trimmed to an exactpredetermined width. in some modern machines, during the operation ofscoring longitudinally, the longitudinal edge trimming is performed'before the corrugated fiberboard continuous sheet is cut to length forindividual box blanks.

The next operation usually accomplishes three functions:

The sheet is trimmed transversely to a desired length, three slots withconnecting score lines are cut on both sides of the sheet to form theindividual top and bottom flaps, and any desired printing is applied tothe surface (usually exteriorly).

Finally, in a fourth operation, the product box blank is folded so thatthe two ends come together and are then joined by taping, gluing, orstapling. This flattened "tube can then be opened up into box form, thebottom flaps folded closed and sealed, the contents placed inside, andthe top flaps folded and sealed.

if the corrugated fiberboard used to make the blanks does not have itsresin treated medium and (optionally) liner members thermoset, a finalblank processing step is preferably performed. Thus, in such event,usually before a blank (such as a flattened tube) is opened into boxform, but after folding,

scoring, slotting, and related operations are completed, a

resulting carton blank is heated to a temperature and for a timesufficient to substantially completely thermoset the phenol-aldehyderesin system impregnated into the medium and (optionally) liner membersof the board. In general, suitable temperatures for this purpose rangefrom about 320 to 450 F. applied for times ranging from about 2 to 10minutes (with higher temperatures requiring shorter cure times). Such athermosetting increases the water resistance properties (e.g. crushresistance, as indicated above) of the product fiberboard and blank madetherewith.

DESCRIPTION OF DRAWINGS The invention is better understood by referenceto the attached drawings wherein:

FIG. 1 is an enlarged, diagrammatic vertical cross-sectional view, someparts thereof broken away, of one embodiment of a corrugated fiberboardconstruction of this invention, and

FIG. 2 is a simplified flow sheet illustrating the method of makingcorrugated fiberboard in accordance with the teachings of the presentinvention.

Turning to FIG. 1, there is seen a corrugated fiberboard construction ofthe present invention which is designated in its entirety by the numerall0. Construction I is seen to incorporate a pair of facing liner sheetmembers 11 and 12. Interposed between liner sheet members 11 and 12 is acorrugated medium sheet member 13. The liner sheet members 11 and 12 areoptionally treated with a phenolic resin as taught herein above, whilethe medium sheet member 13 is treated with a phenolic resin as taughtherein above.

The tips of the flutes in the corrugated medium 13 are bonded to theadjacent faces of respective liner members 11 and 12 by means of anadhesive 14. Conventionally, the adhesive 14 is applied to the tips ofthe flutes during the combining operation of the medium 13 and theliners l1 and 12. After assembly, the construction is heated as abovedescribed to thermoset the adhesive 14 and produce the corrugatedfiberboard 10.

Steps in one embodiment of a process for making a fiberboard 10 areshown in FIG. 2. This block diagram is believed to be largelyself-explanatory particularly in view of the foregoing description so nodetailed explanation thereof is given herein. Observe that FIG. 2 merelyillustrates one mode of practicing the present invention and thatdeviations and variations in accordance with the teachings of thepresent invention are possible without departing from the spirit andscope of this invention.

The machine used to make corrugated fiberboard usually combines into asingle operation the steps of corrugating the medium, applying adhesivesto the flutes thereof, and assembling the so-prepared medium with liner.I-iot pressing of the so-assembled fiberboard is usually alsoaccomplished in the same machine. Although the process embodiment ofFIG. 2 discloses initially curing only the adhesive, it will beappreciated that it is convenient to practice the invention by curingboth the adhesive and the resin for treatment of medium and linermembers before making carton blanks from the fiberboard.

Those skilled in the art will appreciate that the type of corrugatedfiberboard shown in FIGS. 1 and 2 is known to the trade as double facedcorrugated fiberboard since a medium liner is combined with a so-calledinner and so-called outer liner.

Single-faced corrugated fiberboard is made by using a single corrugatedmedium member and a single liner member; double wall corrugatedfiberboard comprises three liners with two corrugated medium membersalternatively spaced between the liners; and triple wall corrugatedfiberboard comprises seven thicknesses and is made by bonding two singlefaced boards into a double-faced board in which there are four linersand three corrugated medium members. All such corrugated fiberboardconstructions are within the contemplation of the present invention.

EMBODIMENTS The following examples are set forth in illustrate moreclearly the principles and practice of this invention to one skilled inthe art and they are not intended to be restrictive but merely to beillustrative of the invention herein contained. All parts are parts byweight unless otherwise indicated.

The following examples illustrate resin systems and adhesives suitablefor use in making products of this invention.

EXAMPLE A A suitable phenol-formaldehyde resole resin for use in thisinvention is prepared as follows:

To parts of phenol in a reaction kettle are added first 180 parts of 50percent formalin and then 4 parts of sodium hydroxide sufficient tobring the pH to about 8.6. The mixture is refluxed for about 3 hours atabout 65 C., while maintaining a reaction pH of about 8.6. Thereafter,this mixture is cooled to about 40 C. This mixture is then neutralizedto a pH of about 7.0 with aqueous diluted hydrochloric acid. Theresulting mixture is dehydrated under vacuum to the desired solids level(see table A below). The product yield is about 270 weight percent basedon starting phenol. The product has a water solubility such that a 55weight percent aqueous solution of resole resin solids can be prepared.The resin characteristics are summarized in table A below.

EXAMPLE B Another suitable phenol-formaldehyde resole resin for use inthis invention is prepared as follows:

To I00 parts of phenol in a reaction kettle are added first 170 parts of50 percent formalin and then 6 parts of calcium hydroxide sufficient tobring the pH to about 8.6. The mixture is refluxed for about 4 hours at62 C. Thereafter, the mixture is cooled to 40. The mixture is thenneutralized to a pH of 7.2 with carbon dioxide. The resin is filtered toremove the calcium carbonate. The product has a water solubility suchthat a 55 weight percent aqueous solution of resole resin solids can beprepared. The resin characteristics are summarized in table A below.

EXAMPLE C Another suitable phenol-aldehyde resole resin for use in thisinvention is prepared as follows:

To 100 parts phenol in a reaction kettle are added parts of 50 percentformalin and 4 parts triethylamine amine as a catalyst. The mixture isrefluxed at about 70 C. for about 4 hours until a free formaldehyde endpoint of 8.6 percent is reached. The resin product is then cooled to 30C. It has a solids content of about 48.0 weight percent. The product hasa water solubility such that a 55 weight percent aqueous solution ofresole resin solids can be prepared. The resin characteristics aresummarized in table A below.

1 Free formaldehyde content determined by the so-called hydroxyb aminehydrochloride method.

1 pH measured at 25 C. using an aqueous solution of about 35 weightpercent total resin solids.

3 Measured by methylol content and methylene bridges pcr aromatic ringusing nuclear magnetic resonance on a sample 01 product.

4 Ash content determined using a 35 weight percent aqueous solution oftogall rei sins at F. at 2 hours and thereafter pyrolyzod for 24 hoursat 1,

EXAMPLE D A modifier solution is prepared by dissolving 30 parts byweight of urea and parts of ammonium chloride in 60 parts of water.

EXAMPLE E A modifier solution is prepared by dissolving 400 parts byweight of urea and 150 parts by weight of ammonium chloride in 600 partsof water.

EXAMPLE F A modifier solution is prepared by dissolving 50 parts byweight urea and 30 parts by weight ammonium sulfate in 100 parts water.

EXAMPLE G A phenol-aldehyde resin system treating solution is made bydiluting 50 parts of the resin of example A with 25 parts of water andthen adding thereto 8 parts of the modifier solution of example D. Theproduct resin system comprises (on a 100 dry weight percent basis) about84 weight percent phenol-formaldehyde resole resin; about 4 weightpercent ammonium salt, and about 12 weight percent urea. The system hasa pH of about 1.5 when in the form of an aqueous solution of about 35weight percent total resin system solids. As thus made, however, thissystem contains about 30 weight percent total resin system solids withthe balance up to 100 weight percent being water.

EXAMPLE H Another phenol-aldehyde resin system treating solution is madeby diluting 100 parts of the resin of example B with 100 parts of waterand adding thereto 12 parts of the modifier solution of example E. Theproduct resin system comprises (on a 100 dry weight percent basis) aboutweight percent phenol-formaldehyde resole resin; about l.5 weightpercent ammonium salt, and about 3.5 weight percent urea. The system hasa pH of about 2.0 when in the form of an aqueous solution of about 35weight percent total resin system solids. As thus made, however, thissystem contains about weight percent total resin system solids, with thebalance up to 100 weight percent being water.

EXAMPLE I Another phenol-aldehyde resin system treating solution is madeby diluting 100 parts of the resin of example C with 100 parts of waterand adding thereto 20 parts of the modifier solution of example F. Theproduct resin system comprises (on a 100 dry weight percent basis) about20 weight percent phenol-folmaldehyde resole resin; about 1.5 weightpercent ammonium salt, and about 4.0 weight percent urea. The system hasa pH of about 2.2 when in the form of an aqueous solution of about 35weight percent total resin system solids. As thus made, however, thissystem contains about 25 weight percent total resin system solids withthe balance up to l00 weight percent being water.

EXAMPLE J A urea-starch-formaldehyde adhesive system for use in thisinvention is prepared as follows:

Two hundred thirty-four pounds of carrier starch are heated at 180 F. in84 gallons of water, cooled to 140 F. and 126 gallons of water added.Four hundred sixty-eight pounds of raw corn starch are then added andmixed to form a uniform dispersion. The pH is adjusted to 7-8 withsodium carbonate. When the temperature drops to about 90 F. One hundredsixty pounds ofa water soluble urea-formaldehyde resin, having a solidscontent of 65 percent, is added and mixed. Im-

mediately prior to use the pH is adjusted to about 5.5 with an acidsalt, e.g., ammonium chloride.

The product adhesive has a total solids content of about 32 weightpercent (starch plus urea-formaldehyde resin) and it contains about 15percent urea-formaldehyde resin solids on total starch.

EXAMPLE K Another suitable urea-starch-formaldehyde adhesive system foruse in this invention is prepared according to the teachings ofexample 2ofU.S. Pat. No. 2,463,148.

The following examples illustrate the manufacture of corrugatedfiberboard of the present invention using the abovedescribed resoleresins and adhesive systems.

EXAMPLE 1 Each side of a 26 pound basis weight medium paper sheet about0.009 inch thick are roller coated with modified phenolaldehyde resinsystem of example G to a total resins content of about 8 weight percentbased on the dry weight of the sheet plus resin. One side of a 42 poundbasis weight Kraft liner paper sheet about 0.009 inch thick is rollercoated with the same resin system to a total resins content of 4 percentbased on the dry weight of the sheet plus resin. The so-treated mediumsheet and liner sheet are each dried to a total volatiles content ofabout 6 percent (as indicated by drying the paper to C. for 10 minutesto determine weight loss).

Next, a medium sheet is corrugated into type B flutes of about 50 perfoot, and the urea-formaldehyde-starch adhesive of example J is appliedto the tips of the flutes of the medium corrugations at the rate ofabout 4 pounds per 1000 ft. of product fiberboard. The medium is thencombined with two pieces of such liner sheet, one on each side of theadhesive treated medium sheet so as to form a corrugated fiberboard.This board is now exposed to a temperature of about 350 F. for about 2seconds to dry and thermoset the adhesive. The product is an example ofacorrugated fiberboard of this invention. A portion of this product isnow exposed to 180 C. for 4 minutes to thermoset resin; this acorrugated fiberboard of this invention.

Each such fiberboard product is now cut, scored, slotted, and formedinto a box blank, after which the blank prepared from the first madefiberboard is subjected to a temperature of about 400 F. for about 2minutes to thermoset the resin.

A container is assembled from a blank made with above made resin curedfiberboard and one is made from a blank made with above made nonresincured fiberboard. The containers are compression tested for strength(top to bottom) ASTM Test Procedure D-642-47.

The treated containers display much greater strength than the untreatedcontainers after testing at (a) 50 percent relative humidity/24 hrs. at72 F., (b) 95 percent humidity/24 hrs. at 72 F., and (c) in water for 24hrs.

EXAMPLE 2 Using the procedure of example 1, but employing a containerassembled from board made in accordance with as the medium a 33 poundbasis weight 0.009 inch thick having a 10 weight percent resin contentand a 5-8 percent volatiles content, and employing as the liner a 69pound basis weight paper (thickness) having a 5 weight percent resincontent and a 5-8 percent volatiles content, similar blanks andcontainers are made and compression tested (top to bottom). Thecorrugated medium has type C flutes ofabout 40 per foot.

The treated containers display much greater strength than the untreatedcontainers after testing at (a) 50 percent relative humidity/24 hrs. at72 F., (b) 95 percent relative humidity/24 hrs. at 72 F, and (c) inwater for 24- hrs.

EXAMPLE 3 A 33 pound basis weight 0.009 inch thick medium sheet isimmersed in a solution of resin of example G and dried. The

product is another example of corrugated medium has type C flutes ofabout 40 per foot. The product sheet has a total resin content of weightpercent based on the weight of the sheet plus resin and a volatilescontent of 5-8 percent. After corrugation, a urea-formaldehydestarchadhesive system of example K is applied to the tips of the corrugationsand then combined with untreated 42 pound basis weight Kraft liner papersheets 0.009 inch thick to form corrugated fiberboard which is thenheated to 340 F. for 3 seconds. The product board is scored, die cut,slotted, and then heated in a forced draft oven for 2 minutes at 400 F.to cure the resin. Another board is made as above, except that theporous medium paper sheet is not treated with resin. The two boards aretested for flat crush strength (ASTM Test Procedure D-l225-54). Thetreated containers display much greater strength than the untreatedcontainers after testing at (a) 50 percent relative humidity/24 hrs. at72 F., (b) 90 percent relative humidity/24 hrs. at 72 F., and (c) inwater for 24 hrs.

The above example clearly shows the superiority in wet strength ofboxboard and containers made in accordance with this invention overthose commercially available.

EXAMPLES 4-6 Using the procedure of example 1, additional corrugatedboxboards are made. In each instance, the medium, the liner, thetreating resin, and the adhesive are as indicated in table lV below. Ineach instance, the product corrugated fiberboard displays excellentresistance to deterioration in strength in the presence of moisture ofwater using ASTM Test Procedure D-1225-D) Similarly, each of thecorrugated fiberboard constructions of this invention made in theforegoing examples l-3 when similarly tested likewise display excellentresistance to deterioration and strength when in the presence ofmoisture as determined by ASTM Test Procedure 1225-54.

modified phenol-aldehyde resin system dry weight basis) ofaphenol-formaldehyde resole having a formaldehyde to phenol mol ratio offrom about 0.9 to 3.0,

b. from about 1 to 5 weight percent (same basis) of at least oneinorganic ammonium salt having a pH of from about 0.8 to 6.5 when in a 5weight percent aqueous solution, and

c. the remainder up to 100 weight percent (same basis) of any given suchsystem being urea,

2. said phenol-formaldehyde resole being characterized by having:

a. a water solubility such that a 55 weight percent aqueous solutionthereof can be prepared,

b. a pH of from about 7 to 9.2 when in the form of an aqueous solutionof about 35 weight percent total resin solids, and Y c. an ash contentof less than about 2.5 weight percent (based on a 35 weight percentsolution of total resin solids).

B. as a liner, a sheet member having a thickness of from about 5 to 20thousandths of an inch and having a grade weight of from about 33 to 120pounds per 1000 sq. ft.,

C. an adhesive comprising a urea-starch-formaldehyde systemcharacterized by: 1 1. having a total urea to total starch weight ratio(based on total adhesive system solids) of about I to 7.

2. containing at least about 1 weight percent (based on total adhesivesystem solids) of combined formaldehyde, and 3. containing at leastabout 70 weight percent of starch (based on total adhesive systemssolids),

D. said corrugated medium sheet member being positioned adjacent saidliner sheet member and being bonded thereto at positions of mutualcontact therebetween by said adhesive, and

TABLE IV Treating resin system Adhesive Medium 1 Liner Amount in mediumAmount in liner Amount Thiek- Grade 'Ihick- Grade Ex. Percent PercentPercent Percent Ex. adhesive Example number ness weight ness weight No.resin volume resin volume N 0. applied 1 4 009 26 16 62 H 12 8 3 5 K 3009 33 15 62 1 10 6 7 8 K 3 .009 33 15 62 U 12 7 J 3 1 Flutes incorrugated medium are Type B (about 60 per foot). Lbs/1,000 it. ofproduct board.

What I claim is: E. such resulting construction having been subjected toa l. A corrugated fiberboard construction adapted to be rigid when wetcomprising:

A. as a medium, a corrugated sheet member having a thickness of fromabout 7 to 15 thousandths of an inch and a grade weight of from about 25to 36 pounds per 1,000 sq. it, said medium sheet member containing fromabout 5 to 15 weight percent (dry weight basis) of a modifiedphenol-aldehyde resin system and said medium sheet member having a totalvolatiles content of from about 5 to 10 weight percent,

1. said modified phenol-aldehyde resin system having a pH in the rangeof from about 0.8 to 6 when in the form of an aqueous solution of about35 weight percent total resin system solids and comprising:

a. from about 80 to 94 weight percent (based on total temperature offrom about 320 F. to 450 F. for, inversely, a time of from about 0.5seconds to 10 minutes.

2. The fiberboard construction of claim 1 wherein said liner sheetmember contains from about 2 to 10 weight percent (dry weight basis) ofsaid modified phenol-aldehyde resin system and said liner sheet memberhas a total volatiles content of from about 5 to 10 weight percent.

3. A box blank prepared from a corrugated fiberboard construction ofclaim 1.

4. A box blank prepared from a corrugated fiberboard construction ofclaim 2.

P040510 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION P t t NDated September 19, Inventor(s) ABRAHAM J. REISMAN It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Please correct the above-identified patent as follows:

Title page, lines 6 and 7, designated item [:73:/,

change from "Assignee Atton Box Board Company,

Alton, Ill. to ---Assignees Alton Box Board Company, Alton, Ill. andMonsanto Company,

St. Louis, Mo.

Signed and sealed this 27th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. said phenol-formaldehyde resole being characterized by having: a. awater solubility such that a 55 weight percent aqueous solution thereofcan be prepared, b. a pH of from about 7 to 9.2 when in the form of anaqueous solution of about 35 weight percent total resin solids, and c.an ash content of less than about 2.5 weight percent (based on a 35weight percent solution of total resin solids). B. as a liner, a sheetmember having a thickness of from about 5 to 20 thousandths of an inchand having a grade weight of from about 33 to 120 pounds per 1000 sq.ft., C. an adhesive comprising a urea-starch-formaldehyde systemcharacterized by:
 2. containing at least about 1 weight percent (basedon total adhesive system solids) of combined formaldehyde, and
 2. Thefiberboard construction of claim 1 wherein said liner sheet membercontains from about 2 to 10 weight percent (dry weight basis) of saidmodified phenol-aldehyde resin system and said liner sheet member has atotal volatiles content of from about 5 to 10 weight percent.
 3. A boxblank prepared from a corrugated fiberboard construction of claim
 1. 3.containing at least about 70 weight percent of starch (based on totaladhesive systems solids), D. said corrugated medium sheet member beingpositioned adjacent said liner sheet member and being bonded thereto atpositions of mutual contact therebetween by said adhesive, and E. suchresulting construction having been subjected to a temperature of fromabout 320* F. to 450* F. for, inversely, a time of from about 0.5seconds to 10 minutes.
 4. A box blank prepared from a corrugatedfiberboard construction of claim 2.